Footstrike characteristics of runners have been studied and evaluated for more than 25 years. These studies have all shown that a majority of the running population, at least 60 to 80%, naturally make initial contact with a running surface over a gait cycle with the heel. These runners are referred to as heel-to-toe runners, heel strikers, or rearfoot strikers. As shown in FIG. 1, rearfoot strikers strike the ground first with the edge of the lateral heel, within the shaded area shown as initial rearfoot strike zone 10.
In 1980, Cavanagh and Lafortune first identified another distinct footstrike pattern in a study of a group of 17 runners. Five (5) of the subjects landed initially in some area 20 of the midfoot, as shown in FIG. 2, in contrast to the remaining twelve (12) who landed on the heel area. Cavanagh, Peter R. and LaFortune, Mario A., “Ground Reaction Forces in Distance Running,” J. Biomechanics, Vol. 13, pp. 397-406 (June 1979), (hereinafter “Cavanagh”). These five runners were identified as so-called “midfoot strikers.”
In Cavanagh, the total contact area over a gait cycle was monitored for both rearfoot strikers and midfoot strikers, once these two categories of runners were identified. Cavanagh found that while the total contact area over a gait cycle for midfoot strikers was largely confined to a central portion of the lateral side of the foot, the total contact area for rearfoot strikers was larger, extending from the initial strike zone 10 in the lateral heel area to a forefoot toe portion of the foot along the longitudinal axis of the shoe in the final “toe-off” phase of the gait. The larger contact area for rearfoot strikers is indicative of the greater percentage of the gait cycle during which a rearfoot striker's foot contacts the ground. Consequently, rearfoot strikers are considered to have a less efficient running gait than midfoot strikers.
Though the midfoot striking technique appears to be superior, studies have shown that the majority of runners are naturally rearfoot strikers. In 1983, for example, in a study of the footstrike characteristics of both recreational runners participating in a 10 k event and elite runners participating in a marathon, it was found that approximately 80% of the runners in each of the events landed on the heel and 20% landed on the midfoot. It was also found, however, that the faster runners in each event tended to be midfoot strikers. Kerr, B. A., Beauchamp, L., Fisher, V. and Neil, R., “Footstrike Patterns in Distance Running,” Biomechanical Aspects of Sports Shoes and Playing Surfaces, pp. 135-142 (University Printing Calgary, Calgary A B, 1983).
Other studies have also suggested a correlation between speed and running gait. For example, it has been found that a great number of runners who may appear to be heel strikers at a comfortable running pace, change to a midfoot striking gait at increased speeds, largely due to an involuntarily shift forward of body weight. Williams, Keith R., “Biomechanics of Running,” Exercise and Sport Sciences Reviews, Vol. 13, pp. 299-441 (1985).
Serious runners have become increasingly aware of the advantages of implementing a midfoot striking gait as outlined in these and other studies. These advantages include reduced incidences of injury in addition to increased speed and efficiency. McClay, I. and Williams, D., “Lower Extremity Mechanics in a Converted Forefoot Strike pattern in Runners,” North American Congress on Biomechanics, Waterloo, Canada (Aug. 14-18, 1998). Consequently, many runners have converted or attempted to convert from their natural rearfoot striking gait to this midfoot striking technique.
Nicholas Romanov, who developed a now well-known technique of running trademarked as POSE®, has been one of the strongest advocates for teaching this midfoot striking running technique as the preferred running gait. Romanov's technique requires the runner to land on the midfoot, with the supporting joints flexed at impact, and to then use the hamstring muscles to withdraw the foot from the ground, relying on gravity to propel the runner forward. In addition to outlining the technique, Romanov also developed a roadmap of exercises for how a runner could convert from the typical heel strike running pattern to the POSE® running technique. Arendse, R. E, Noakes, T. D., Romanov, N., Schwellnus, M. P., and Fletcher, G., “Reduced Eccentric Loading of the Knee with the Pose Running Method,” Medicine & Science in Sports & Exercise, Vol. 36(2), pp. 272-277 (February 2004).
Midfoot strikers, therefore, fall into the following three basic categories: those that inherently employ a midfoot striking gait independent of speed; runners that are rearfoot strikers at a comfortable running pace, but naturally shift to midfoot or even forefront striking as their speed increases; and those that are inherently rearfoot strikers but have converted or are trying to convert to a midfoot striking gait for various reasons.
Though there have been some attempts in the footwear industry to fashion a shoe that is conducive to midfoot striking, there is a need for an improved running shoe for both natural and converted midfoot strikers.